Republicans will lose unified control of the federal government in 2019, as Democrats will take control of the House of Representatives after their midterm victory on Tuesday. It's a highly welcome repudiation of President Trump's bigotry and 1-percenter policy.

But House Democrats better be ready for bitter trench war. America is in an extremely parlous state, and they are the only ones at the federal level who can defend our democratic institutions from the suppurating political and moral corruption of the Republican Party.

It's already starting, with Trump pushing out Attorney General Jeff Sessions (who had recused himself from the Robert Mueller investigation) on Wednesday and naming Matthew Whitaker, an utter toady who won't interfere with Trump if he tries to obstruct justice, as acting attorney general. Rep. Jerry Nadler (D-N.Y.), who will be chair of the House Judiciary Committee next year, has the right idea:

Americans must have answers immediately as to the reasoning behind @realDonaldTrump removing Jeff Sessions from @TheJusticeDept. Why is the President making this change and who has authority over Special Counsel Mueller’s investigation? We will be holding people accountable. https://t.co/weykMuiCxm

With the House majority comes two important powers: authority over the budget and subpoenas. The first is simple — the House is where appropriations come from. That means Democrats get substantial leverage over what gets funded, which they should use to stop any more rollbacks of social insurance or more tax cuts for the rich.

The second will be more complicated. House committees can conduct investigations and have subpoena power. (Ironically, due to a Republican rule change in 2015, most Democratic committee chairs can issue these unilaterally, so that will make things a bit easier.) Protecting Mueller will be challenging, as Richard Nixon himself proved in the infamous Saturday Night Massacre that got rid of Watergate prosecutor Archibald Cox. But on the other hand, that eventually helped destroy Nixon: The firing was ruled illegal, led to the appointment of a new special prosecutor, and badly dented Nixon's popularity. Democrats must do their utmost to keep Mueller in his post, or failing that, keep investigating how he was fired and what he found.

Beyond looking into White House interference with the special counsel, probably the most important thing for Democrats to investigate is possible election-rigging on the part of state Republican officials (most notoriously Georgia Secretary of State Brian Kemp), as Hamilton Nolan argues. A close second is Trump's monumental corruption — Dems need to get his tax returns, pursue an Emoluments Clause challenge to his rampant profiteering off the presidency, expose his possibly-illegal hush money payments to porn stars, and investigate his ties to Saudi Arabia and Russia, just for starters.

Now, it will be difficult to get sustained attention on this stuff. Every day Trump easily gets the media to follow the bouncing ball of whatever new outrageous lie or bug-eyed lunacy he has come up with. Democrats must cultivate a theatrical sense to match — I would suggest finding some lead investigators with ambition and camera skills, picking two to three clear stories, and hammering them over and over and over. Constant repetition and simple themes are key to getting distracted swing voters to pay attention.

Democrats should also be ready for the strong possibility that Trump and other Republicans will flagrantly refuse to obey subpoenas. Legal options will have to be explored.

But the most important thing Democrats have to do is fight, fight, and fight some more, at the federal, state, and local level. This will require ditching one of the signature notions of moderate liberalism (as espoused by Steven Pinker, Barack Obama, and others): the idea that the story of America is slow and steady progress, from a darker past to a progressively better future.

Even a cursory glance at history casts severe doubt on this idea. On many occasions — 1876, the mid 1970s, or 2003 — American institutions have firmly embraced appalling evil. As Tom Scocca writes, in the case of Redemption, the terrorist overthrow of the Reconstruction multi-racial democracy that led to 90 years of Jim Crow tyranny in the South, the evil was tolerated or justified by intellectuals and virtually the whole political elite. The same is true of the invasion of Iraq, a baldly illegal and unjustifiable war of aggression that caused several cataclysmic humanitarian disasters.

Conversely, when things have changed for the better — say 1865, 1933, or 1965 — it has always been the result of a ferocious political battle. The slaves were freed only after a bloody civil war that killed 750,000 people. The tyrannical plutocracy of the Gilded Age and the Lochner Doctrine, and the Jim Crow reign of terror, were overthrown only after years of grinding mobilizing and organizing, in the teeth of routine brutal violence.

There is basically no automatic process by which Trump and the odious political movement he represents can be removed from the body politic. It will take struggle and political conquest.

In 2019, there is certain to be a strong push from D.C. centrists — who would strongly prefer pretending everything is fine to actually making it so — to not fuss too much over Trump. They will demand bipartisan compromise, moderation for its own sake, and austerity programs to cut the budget deficit (especially cuts to Medicare and Social Security).

This temptation must be resisted. As Franklin Roosevelt once said, "To some generations much is given. Of other generations much is expected." House Democrats do not have time to fiddle around with deficit projections 80 years hence. It's time to start defending American democracy.